Electrochromic (EC) materials are a subset of the family of chromogenic materials, which includes photochromic materials, and thermochromic materials. These are materials that change their tinting level or opacity when exposed to light (photochromic), heat (thermochromic) or electricity (electrochromic). Chromogenic materials have attracted widespread interest in applications relating to the transmission of light.
An early application for chromogenic materials was in sunglasses or prescription eyeglasses that darken when exposed to the sun. Such photochromic materials were first developed by Corning in the late 1960s. Since that time, it has been recognized that chromogenic materials could potentially be used to produce window glass that can vary the amount of light transmitted, although the use of such materials is clearly not limited to that prospective application. Indeed, EC technology is already employed in the displays of digital watches.
With respect to window glass, EC materials are exciting because they require relatively little power to produce a change in their tinting level or opacity. EC windows have been suggested for use in controlling the amount of daylight and solar heat gain through the windows of buildings and vehicles. Early research indicates that EC window technology can save substantial amounts of energy in buildings, and EC glazings may eventually replace traditional solar control technology such as tints, reflective films, and shading devices (e.g., awnings). Because of their ability to control lighting levels and solar heat gain, EC windows have the potential of reducing the annual U.S. energy consumption by several quadrillion (1015) BTUs, or quads, which is a substantial decrease relative to current consumption rates.
Several different distinct types of EC materials are known. The primary three types are inorganic thin films, organic polymer films, and organic solutions. For many applications, the use of a liquid material is inconvenient, and as a result, inorganic thin films and organic polymer films appear to be more industrially applicable.
To make an EC device that exhibits different opacities in response to a voltage, a multilayer assembly is required. In general, the two outside layers of the assembly are transparent electronic conductors. Within the outside layers is a counter-electrode layer and an EC layer, between which is disposed an ion conductor layer. When a low voltage is applied across the outer conductors, ions moving from the counter-electrode to the EC layer cause the assembly to change color. Reversing the voltage moves ions from the EC layer back to the counter-electrode layer, restoring the device to its previous state. Of course, all of the layers are preferably transparent to visible light. Both inorganic and organic ion conductive layers are known.
In order to be useful in a window application, or in a display application, EC materials must exhibit long-term stability, rapid redox switching, and exhibit large changes in opacity with changes of state. For inorganic thin film based EC devices, the EC layer is typically tungsten oxide (WO3). U.S. Pat. Nos. 5,598,293, 6,005,705, and 6,136,161 each describe an inorganic thin film EC device based on a tungsten oxide EC layer. Other inorganic EC materials, such as molybdenum oxide, are also known. While many inorganic materials have been used as EC materials, difficulties in processing and slow response time associated with many inorganic EC materials have created the need for different types of EC materials.
Conjugated, redox-active polymers represent one different type of EC material. These polymers (cathodic or anodic polymers) are inherently electrochromic and can be switched electrochemically or chemically between different color states. A family of redox-active copolymers are described in U.S. Pat. No. 5,883,220. Another family of nitrogen based hetrocyclic organic EC materials is described in U.S. Pat. No. 6,197,923. Research into still other types of organic film EC materials continues, in hopes of identifying or developing EC materials that will be useful in EC windows.
While EC windows, or smart windows as they are sometimes called, are expected to represent a significant commercial application of EC technology, one additional potential use of an EC is in producing displays, sometimes referred to smart displays, or digital windows (DWs). One promising application for DW systems relates to deoxyribonucleic acid (DNA) chip reading. For more efficient DNA chip reading/writing technology, it would be desirable to replace expensive custom photomasks in the photosynthesizing of oligonucleotides in DNA array fabrication. There are several reasons why it would be desirable to develop a new method applicable to this technology for use in oligonucleotide chip manufacturing. Specifically, oligonucleotide chips have become increasingly important, as more genomes of organisms are sequenced. Accordingly, there is a need to develop a low cost, easy to use, high-density DNA arranger and system for reading unknown DNAs, based on surface plasmon resonance, with higher lateral resolution that is provided in current systems.
A suitable system for such an application should employ a switchable window that is readily changed from transparent to nontransparent (e.g., to dark blue) by varying an electric potential polarity (anodic EC polymer sides have a negative polarity and a positive polarity, respectively). These switchable window laminate materials should be convertible to a digital (pixel) array having a size typically ranging from about submicron to about 50 microns, and each array unit should be independently controlled to change from a transparent to a nontransparent state. By combining this functionality with an surface plasmon resonance (SPR) system serving as a real time analyzer of unknown molecules, including DNA sequences and characterizations of unknown molecules and in vivo and in vitro cell-cell interactions. Such a high resolution SPR system should then be useful for analyzing unknown molecules and DNA sequences on a real-time basis, at faster speed than is currently possible, by scanning through one group of molecules after another, i.e., by opening the corresponding digital window (DW) unit. With such a system, the speed with which unknown molecules (and DNA and RNA sequences) can be analyzed will be much enhanced, compared with conventional prior art techniques.
An additional exciting application of EC technology relates to the use of EC devices for display technologies, beyond the somewhat limited application of monochromatic displays now used in digital watches. EC devices that can controllably transition between more than two color states offer the potential of flat panel multicolor displays, using the digital pixel array noted above.